1. Field of the Invention
The present invention relates to a substrate rotation type treatment apparatus that holds substrates such as semiconductor wafers, liquid crystal display glass substrates, photo-mask glass substrates, optical disk substrates in a horizontal posture to cause the substrates to rotate about a vertical axis, and supplies to the substrate surface treatment liquids such as cleaning fluids, coating solutions, and developers to make the substrate treatment such as cleaning, coating, and development.
2. Description of the Related Art
When substrates such as semiconductor wafers are held in a horizontal posture with a spin chuck to be brought in rotation about a vertical axis, and a treatment liquid, for example, a cleaning fluid, e.g., pure water is supplied to the substrate surface to make the cleaning treatment of the substrates, the cleaning fluid having been supplied on the substrate surface spreads to the substrate edge due to a centrifugal force, and the cleaning fluid having been used is diffused from the substrate edge to the surroundings. There is provided around a substrate, which is held by a spin chuck, a cup so as to surround the sides and the under side of the substrate. The used cleaning fluid having been diffused from the substrate to the surroundings impinges on the inside wall surface of a cup to be collected, flows down on the cup inside wall surface to be collected at the cup bottom, and is discharged from a drain, which is provided in the cup bottom, through a drain pipe to be recycled.
A cup for collecting a treatment liquid having been diffused from a substrate to the surroundings has been conventionally made of plastic materials such as fluororesin, e.g., polytetrafluoroethylene (PTFE), polyvinylchloride (PVC), and polypropylene (PP), or metal materials such as stainless steel. At present, however, most cups are made of resin. A main function of this cup is to prevent a treatment liquid having been diffused from the substrate to the surroundings from being diffused also to the outside of the substrate treatment section, as well as to collect the treatment liquid to cause it to flow to a drain in the cup bottom. Nevertheless, a plastic material, especially, fluororesin that forms a cup is water-repellent (hydrophobic), and an inside wall surface of the cup will be repellent to a hydrophilic treatment liquid such as cleaning fluid, e.g., pure water when the treatment liquid impinges thereon.
FIGS. 4-A and 4-B are schematic diagrams showing the schematic construction of substrate rotation type treatment apparatuses. In the drawings, reference numeral 1 designates a spin chuck that holds a substrate W in a horizontal posture. Numeral 2 designates a rotary shaft that supports the spin chuck 1 holding a substrate W to cause it to rotate about a vertical axis. Numeral 3 designates a cup that collects a treatment liquid. Numeral 4 designates a drain portion that discharges the treatment liquid, and recycles it. When the cups 3 is made of a hydrophilic material, as shown in FIG. 4-B, a hydrophilic treatment liquid having been diffused from the surface of a substrate W to the surroundings to impinge on the inside wall surface of the cup 3 spreads forming a thin film on the inside wall surface to flow down to the bottom of the cup 3, and is discharged through the drain portion 4. In contrast, when the cup 3 is made of a water-repellent material, as shown in FIG. 4-A, a treatment liquid having been diffused from the surface of a substrate W to the surroundings to impinge on the inside wall surface of the cup 3 is splashed on the inside wall surface, and a part of it will adhere to the surface of a substrate W again. At this time, a problem arises in that when a treatment liquid such as used cleaning fluid contains impurities, the impurities in the treatment liquid becomes particles to be contamination-causing substances of a substrate W. Moreover, a further problem arises in that when a treatment liquid adheres to the inside wall surface of the cup 3 to be dried, and treatment liquid constituents are accumulated during the treatment of a number of substrates, the accumulated constituents become particles to adhere to the surface of a substrate W along with the treatment liquid having been splashed on the inside wall surface to be contamination-causing substances.
To overcome this problem, it has been carried out that a cup made of a water-repellent material is made hydrophilic. Several methods of making hydrophilic include, for example, as disclosed in the Japanese Patent Publication (unexamined) No. 258249/1998, a method that material properties itself is improved to be hydrophilic by mixing a substance for making hydrophilic into resin material at the time of making a cup of a plastic material by molding, or another method that the inside wall surface of a cup is made hydrophilic by a hydrophilic material being deposited on the inside wall surface of a cup forming a thin film.
However, in a cup which material properties itself is improved to be hydrophilic by mixing a substance into resin material, a problem still exists in that the mixed substances will be eluted in the use of a long time period to become contamination-causing substances of a substrate. Moreover, in a cup on the inside wall surface of which a hydrophilic material is deposited forming a thin film, a problem exists in that the thin film of hydrophilic material comes off from the inside wall surface in the use of a long time period to become contamination-causing substances of a substrate.